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CS1 Python Subgoals

Section 4.7 If Statements

Subgoals for Evaluating Selection Statements.

  1. Diagram which statements go together by indentation
  2. For conditional, determine whether expression is true
    1. If true, follow true branch
    1. If false, follow next elif/else branch or exit conditional if no else branch
  3. Repeat step 2 as necessary

Subsection 4.7.1

Given the following declarations:
alpha = 2
beta = 1
delta = 3
eta = 0
gamma = 0
Evaluate these statements and determine the value of all variables used.
The figure shows the two if statements, each highlighted in a different color.
Figure 4.7.1. 
if alpha > beta:
    eta = alpha + 2
if alpha > delta:
    gamma = alpha + 5

Subsection 4.7.2 1. Diagram which statements go together by indentation

There is a single indented statement in the body of the first if statement, and a single indented statement in the body of the second if statement.

Subsection 4.7.3 2. For conditional, determine whether expression is true

Because there are 2 sequential if-statements, we start with the first one, and then repeat SG2 and SG3 for the other.
First we evaluate alpha > beta:
2 > 1 is True.

Subsection 4.7.4 3. If true, follow true branch; If false, follow next elif/else branch or exit conditional if no else branch

The condition is True, so we execute the true branch.
eta = alpha + 2
= 2 + 2
= 4
The figure shows the first if statement, highlighted in blue.
Figure 4.7.2.

Subsection 4.7.5 SG2: For if statement, determine whether expression is true

Because there are 2 sequential if-statements, we need to repeat SG2 and SG3 for the second if-statement in the sequence.
First we evaluate alpha > delta:
2 > 3 is False

Subsection 4.7.6 SG2.2: If false, follow next elif/else branch or exit conditional if no else branch

The condition is FALSE and there is no else branch, so we do nothing.
The figure shows the second if statement, highlighted in yellow.
Figure 4.7.3.
Answer.
alpha = 2, beta = 1, delta = 3, eta = 4, gamma = 0

Practice Pages.

  • [cross-reference to target(s) "evaluate_conditional-we3-p1" missing or not unique]
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